Submenus Not Displaying

I’m still pretty early in building this site, so it may look pretty empty, but I’ve configured a menu that’s supposed to have drop-down sub-menu items under About, Read, and Explore. I’ve checked inspect element to see that they should be there, combed through my theme CSS for anything that might be turning off the visibility of sub-menus, tried (and then commented out) custom CSS to ensure their visibility, cleared my page cache, browser cache and cookies, flushed my DNS cache, restarted my browser, checked in several browsers (Chrome, Firefox), ensured WordPress, browsers, and all plugins and themes are up to date, deactivated (and re-activated) all plugins, ensured I have them set them up properly as sub-menu items, etc. I still can’t see my sub-menus. Any advice?

Thanks so much! ??

The page I need help with: [log in to see the link]